diff --git a/rebuild.php b/rebuild.php
index 675999c..cdc19a9 100644
--- a/rebuild.php
+++ b/rebuild.php
@@ -29,6 +29,7 @@ function mkthumbnail($src_file, $dest_file, $width, $height) {
 	$im = imagecreatefromstring(file_get_contents($src_file));
 	
 	$dest = imagecreatetruecolor($width, $height);
+	imagefilledrectangle($dest, 0, 0, $width, $height, imagecolorallocate($dest, 0xFF, 0xFF, 0xFF));
 	
 	$scale = max( $width/$src_width, $height/$src_height ); // overscale + crop